| depending on your sons age the 50cc-70cc-90cc pitbikes from motoworks are reasonable quality for the price & would withstand alot more punishment
(ISO9002 CERTIFICATION and CE COMPLIANCE) witch is alot more than some sellers offer & with the semi auto gearbox they learn gearshifts without a clutch
the 90cc bikes are fairly quick around 80kph max with a light rider & stock gearing so keep this in mind when looking for a upgrade
(the 50cc are smaller) the 90cc are much the same as the 125s frame with 10 & 12 inch wheels
the small cag powered bikes are a good learners bike but if jumped or treated rough they are prone to breaking the frame, as the suspension is only a spring loaded front & rear with no dampener the frame absorbs a majority of the shock from the bumps | 
